4.6 Logical Values

Octave has built-in support for logical values, i.e., variables that
are either true or false. When comparing two variables,
the result will be a logical value whose value depends on whether or
not the comparison is true.

The basic logical operations are &, |, and !,
which correspond to “Logical And”, “Logical Or”, and “Logical
Negation”. These operations all follow the usual rules of logic.

It is also possible to use logical values as part of standard numerical
calculations. In this case true is converted to 1, and
false to 0, both represented using double precision floating
point numbers. So, the result of true*22 - false/6 is 22.

Logical values can also be used to index matrices and cell arrays.
When indexing with a logical array the result will be a vector containing
the values corresponding to true parts of the logical array.
The following example illustrates this.

data = [ 1, 2; 3, 4 ];
idx = (data <= 2);
data(idx)
⇒ ans = [ 1; 2 ]

Instead of creating the idx array it is possible to replace
data(idx) with data( data <= 2 ) in the above code.

Logical values can also be constructed by
casting numeric objects to logical values, or by using the true
or false functions.

Return a matrix or N-dimensional array whose elements are all logical 1.
If invoked with a single scalar integer argument, return a square
matrix of the specified size. If invoked with two or more scalar
integer arguments, or a vector of integer values, return an array with
given dimensions.

Return a matrix or N-dimensional array whose elements are all logical 0.
If invoked with a single scalar integer argument, return a square
matrix of the specified size. If invoked with two or more scalar
integer arguments, or a vector of integer values, return an array with
given dimensions.